The present invention relates to a method for the preparation of a metal compound in a fine particulate form or, more particularly, to a method for the preparation of a metal compound such as a halide, oxide and composite metal compound, i.e. compounds of at least two kinds of metallic elements, in a fine particulate form.
Fine powders of a metal oxide, for example, are widely used as a base material for the preparation of various kinds of ceramic-based electronic components by utilizing their unique properties. Several methods are known in the prior art for the preparation of a fine metal oxide powder, of which a typical method is the production of particles of a metal oxide in a vapor phase such as the so-called CVD method. A problem in the conventional vapor-phase methods is that the density of the metallic atoms in the vapor phase cannot be high enough so that the efficiency of the method also cannot be high. In addition, the vapor-phase reaction requires a large amount of energy in the form of, for example, light, plasma, electron beams, heat and the like resulting in high costs for the production with a problem in energy saving.
A method is known to prepare fine metal particles by the pyrolytic decomposition of a metal compound in the vapor phase. For example, Japanese Patent Kokai 60-51539 teaches a method for depositing fine metal particles from the vapor phase. Chemistry and Industry, volume 15, page 247 (1985) teaches a method in which an organometallic compound in the vapor phase is decomposed by means of laser beam irradiation.
These prior art methods by the decomposition of a metal compound in the vapor phase are disadvantageous economically and in respect of the product quality since, when the energy for the decomposition is given by a laser beam, at least one photon is required to effect the decomposition reaction to produce a molecule of the metal particle so that the costs for the energy are very great in view of the expensiveness of the laser beam per unit energy even by setting aside the problems in the difficulty encountered in the control of the reaction and formation of a relatively large amount of by-products.
Fine particles of a metal halide can be prepared by bringing a purified metal into contact with a halogen gas at an elevated temperature so that the metal directly reacts with the halogen to produce a metal halide in a fine particulate form. This method is also economically disadvantageous because of the large consumption of the thermal energy.